A number of europium compounds with long fluorescent lifetimes have been synthesized and demonstrated to be useful as molecular probes of cell function in both microscopic analysis and flow cytometry. These compounds have been successfully conjugated to isothiocyanate and used to label and analyze cellular proteins in ethanol fixed cells. Results were comparable to those obtained with fluorescein isothiocyanate; however the signals from the europium labeled cells were many times more intense. Studies in progress are designed to develop conditions for the labeling the cells with Hoechst 33342 for DNA and europium bound to protein, providing preliminary data for the use of the europium in autofluorescence-free, immunofluorescence labeling.